Various processes have been used to prepare aromatic amine compounds from the corresponding aromatic nitro compounds. Such processes include catalytic hydrogenation, which generally employs high purity catalysts at increased temperatures and pressures; and reduction with iron in dilute hydrochloric acid, which requires extensive product purification as well as disposal of the iron hydroxide sludge which is a by-product.
An electrochemical process has also been developed wherein reduction of the nitro compound is carried out in an aqueous strong acid electrolyte in the presence of a catalytic amount of a redox system, such as that provided by salts of Ti.sup.+4 and the reduced species thereof comprising salts of Ti.sup.+3, see, e.g., Noel et al., J. Applied Electrochemistry 12 (1982) 291-298. However, the process is impracticable where the starting material or product has low solubility in the acid electrolyte and adheres to or complexes at the electrode, causing a decline in current efficiency. A so-called two-stage electrochemical process has therefore been proposed, Noel et al., Indian J. Tech. 19 (1981) 100-101, wherein titanous(III) sulfate salts, having been obtained by electrochemical reduction of titanic sulfate, Ti(SO.sub.4).sub.2, are then employed to chemically reduce the starting aromatic nitro compound. However, Noel and co-workers indicate that titanic sulfate is unstable in low acid solution, and an acid concentration of at least about 10% (wt./vol.) must therefore be maintained to prevent hydrolysis of the titanic sulfate and precipitation of the resulting hydrolyzed titanium compounds. It was further indicated that titanous(III) sulfate obtained by reduction of titanic sulfate has low solubility in aqueous solution and precipitates at concentrations exceeding about 0.5 N. Accumulated undissolved solids at the electrodes can significantly reduce current efficiency.